The present invention relates to joint prosthesis elements, to a kit for putting joint prosthesis elements into place, and to a method of manufacturing said joint prosthesis elements.
Numerous diseases such as arthrosis or rheumatism, and certain types of accident, lead to various joints deteriorating, and in particular large joints such as the hip, the knee, the shoulder, etc. Such problems or accidents give rise more particularly to destruction of cartilage constituting the surface of the joint. Such deterioration, in particular of cartilage, can lead to the patient who is a victim thereof being seriously handicapped or even badly incapacitated.
In this field, prosthesis elements for use in the knee or hip joint are well known.
With present day techniques, the prosthesis elements used under such circumstances require considerable resection of the joint surfaces, with such resection giving rise either to a plane surface being formed at the end of the bone concerned, or else to a plurality of plane surfaces being formed at angles to one another and constituting an approximation to the real surface of the joint.
Prosthesis elements of that type require a large amount of bone resection in order to be put into place. Such resection in turn requires expensive surgical equipment to be implemented in order to define accurately the plane or planes of the surface of the resection to be performed. In addition, since the resection surface is plane or constituted by a plurality of plane portions, it is necessary to provide anchoring for the prosthesis element that penetrates very deeply into the portion of bone that is associated with the joint surface in order to hold the prosthesis in place. Anchor elements such as screws, pins, studs, etc. require large anchoring holes to be bored in the bone to be treated. Such large boring or drilling in turn requires expensive surgical equipment to be implemented. In addition, the large amount of boring or drilling in the bone can give rise to damaging consequences for that portion of the bone which is subjected to such perforation, in particular concerning its mechanical strength when stresses are applied to the bones constituting the joint when movements are effected, since the length of the anchoring element transfers the force to a zone of the bone that is not intended to withstand such force.
In addition, in the event of a large and substantially plane resection, the thrust of the prosthesis on the resection surface is unsatisfactory since said surface is essentially constituted by spongy bone, and the thrust against the cortical peripheral of the bone is insufficient for taking up the forces.
In addition, known prosthesis elements do not give practitioners a wide enough range of options for providing the degrees of freedom chosen for the joint. Finally, the means used for anchoring such prostheses continue to remain a source of concern with respect to their strength, their stability, and their wear.
An object of the present invention is to provide prosthesis elements for various joints of the human body, which elements require only limited resection of the joint surface while providing very effective anchoring on the portion of bone concerned, and require only the simplest of surgical equipment for putting them into place. Another object of the invention is to provide such a joint prosthesis element which, when all the ligaments of the joint remain intact, makes it possible to restore to the patient all of the degrees of freedom of a healthy joint.
Another object of the invention is to provide a prosthesis element which improves transmission to the bone of the forces applied to the prosthesis.
To achieve this end, the invention provides a joint prosthesis element for fixing to the joint surface of one of the bones of the joint after said joint surface has been subjected to appropriate resection defining a projecting rim over at least a portion of its outline, characterized in that said prosthesis element is defined by a contact surface for co-operating with the prosthesis element of the other bone of the joint, said contact surface being substantially identical to the anatomical joint surface, a fixing surface for fixing to the resection of the joint surface, and a peripheral surface interconnecting said contact and fixing surfaces, said peripheral surface being designed, at least in part, to co-operate with the projecting rim of said resection, which rim corresponds to the cortical portion of the bone, said fixing surface being provided with fixing means, the distance between said contact and fixing surfaces in the central zone thereof and in a fixed direction being substantially constant, said peripheral interconnecting surface including at least some portions that flare relative to said fixing direction from the fixing surface towards the contact surface or from the contact surface towards the fixing surface, whereby said peripheral surface portions bear against the corresponding portions of the rim of said resection.
It will be understood that the prosthesis element is held securely in place on the hinge surface of the bone after resection, in particular because of the shape of the contact surface on the portion of the joint surface that has been subjected to resection and because of the presence of the peripheral surface of the prosthesis element which co-operates with the rim projecting from the resection. As a result, only a relatively small anchoring element need be provided that penetrates a short distance only into the bone, or a layer of adhesive or sealing material, to completely prevent the prosthesis element from moving in any way on the end of the bone.
The invention also provides a kit for putting joint prostheses into place on a joint surface of one of the bones of said joint, the kit being characterized in that it comprises:
a set of similar ones of said prosthesis elements that differ in certain dimensions, each prosthesis element having a contact face for co-operating with a prosthesis of another type fixed on the other bone of said joint, a fixing face for fixing on said joint surface of the bone after it has been subjected to appropriate resection, said fixing face being provided with at least one anchoring element projecting from said face, and a peripheral surface interconnecting said contact and fixing surfaces, each prosthesis element being of substantially constant thickness between said two faces;
a first set of template-forming means for the outline of the resection, each template being associated with one of the prosthesis of the set, each outline template having means for tracing the outline of the resection to be made, said outline corresponding to the periphery of said prosthesis element;
a set of template-forming means for the anchoring holes, each template-forming means being associated with one of the prosthesis elements of the set, each anchoring hole template including means for positioning relative to the outline of the resection and means for tracing the location of the, or each, anchoring hole associated with the anchoring elements;
a first set of instruments, for milling, for making said resection within said outline and for controlling milling parameters;
a second set of instruments, for boring, for making said anchoring holes and controlling the boring parameters; and
means for providing assistance in guiding the displacement of said instruments in such a manner that the milling instruments are displaced at least along said outline in such a manner that their axes remain substantially parallel to a fixed direction, said direction being tied to said templates, and in such a manner that the drilling instruments are held on the same drilling axis.
It will be understood that by using physical or optical templates enabling the outline of the resection to be traced and enabling the anchoring hole(s) of the prosthesis element to be positioned, and by using milling to perform the resection, a resection is indeed obtained that makes it possible to use a prosthesis element whose peripheral surface co-operates mechanically with the rim projecting from the resulting resection.
More generally, it will be understood that in its various aspects the invention makes it possible to use prosthesis elements for various joints that are of a shape coinciding with the resection performed by the surgeon when the prosthesis elements are put into place. It will also be understood that because of the substantially constant thickness of such prosthesis elements and because of the peripheral surfaces of such prosthesis elements bearing against the corresponding rims of the resections, prosthesis elements are prevented from moving in a manner that does not require a large amount of anchoring to be provided to hold the prosthesis element on the bone in question, and in particular the anchoring that is provided no longer penetrates a long way into the bone.
The invention also provides a method of manufacturing the above-defined joint prosthesis element, the method being characterized in that it comprises the following steps:
taking a bone having the exact shape of the joint surface of a natural bone for which the prosthesis is to be made;
milling a portion of the extremity of the bone in said joint surface while maintaining a constant milling direction so as to define a milled central zone and a peripheral surface, the depth of milling being substantially constant in said central zone, said peripheral surface defining at least in part a rim that projects from said central zone in the milling direction;
making a mold having a mold cavity that is defined firstly by a first surface defining the contact surface and secondly by a second surface constituted by the fixing surface and said peripheral surface that result from the milling;
putting a molding material into said mold so as to take the shape of the mold cavity;
unmolding the resulting piece, thereby obtaining a prototype for said prosthesis element; and
making said prosthesis element from said prosthesis.
The method of manufacturing prosthesis elements makes it possible to give the contact face of the prosthesis element a shape that is identical or quasi-identical to that of the anatomic joint surface prior to resection. This disposition is particularly advantageous when the ligament system of the joint remains intact in the patient being fitted with the prosthesis. In contrast, when the ligament system has been affected and the anatomical degrees of freedom need to be limited accordingly, it is possible to give the contact surface of the prosthesis element a modified shape having greater congruence with the contact surface of the associated prosthesis element so as to limit the relative movements that re possible between the bones forming the joint.
In a first implementation, the fixing means are pegs of generally conical shape penetrating into same-shape anchoring holes.
In a second implementation, the fixing means comprise an anchoring element of dove-tailed shape connected to the central portion of the fixing surface. Under such circumstances, the anchoring hole or orifice is complementary in shape to the anchoring element. To enable the prosthesis element to be put into place, it will be understood that the anchoring hole must open out at one end while it is closed at its other end by bone that has not been subject to resection. Under such circumstances, anchoring advantageously further includes a screw or pin engaged in the free end of the anchoring element in order to prevent the prosthesis element from moving in translation.
In a third implementation, the fixing means comprise a layer of adhesive or sealing material.